Factor V Leiden (G1691A), the Prothrombin 3’-Untranslated Region Variant (G20210A) and Thermolabile Methylenetetrahydrofolate Reductase (C677T): A Single Genetic Test Genotypes all Three Loci – Determination of Frequencies in the S. Wales Population of the UK

COVID-19 spreading across world correlates with C677T allele of the methylenetetrahydrofolate reductase (MTHFR) gene prevalence

Background

Homocysteine assessment has been proposed as a potential predictive biomarker for the severity of COVID‐19 infection. The purpose of this review was to analyze the correlation between the prevalence of MTHFR C677 T gene polymorphism and COVID‐19 incidence and mortality worldwide.

Methods

Data regarding MTHFR C677 T gene mutation were obtained from the interrogation of the Genome Aggregation Database (genomAD), which is publicly available from the web“https://gnomad.broadinstitute.org.” COVID‐19 cases, including prevalence and mortality, were obtained from“https://www.worldometers.info/coronavirus” 27 August 2020.

Results

There is a clear trend toward the worldwide prevalence of MTHFR 677 T and COVID‐19 incidence and mortality. The prevalence of MTHFR677 T allele in the Latino population, and the incidence and mortality for COVID‐19 was higher for this ethnic group than that reported for most other populations globally. Statistical analysis showed a relatively strong correlation between C677 T and death from coronavirus.

Conclusions

Genetic polymorphism of MTHFR C677 T may modulate the incidence and severity of COVID‐19 pandemic infection.

Distribution of MTHFR C677T Gene Polymorphism in Healthy North Indian Population and an Updated Meta-analysis

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme of folate pathway. Several polymorphisms were reported in MTHFR gene but C677T polymorphism is most studied and it has been reported to be risk factor for several diseases/disorders. The present study was designed to explore the frequency of MTHFR C677T polymorphism in North Indian healthy population. In addition to this a meta-analysis of published articles was also performed to estimate the global prevalence of MTHFR C677T polymorphism. A total of 1000 unrelated healthy subjects were selected for MTHFR C677T polymorphism analysis. Different databases were searched for eligible articles. Prevalence proportion with 95 % CI was used to determine global prevalence of T allele and TT genotype. Meta-analysis was performed by Open meta-analyst. In 1000 blood samples analyzed, the frequency of T allele and TT genotype was 11 and 1 % respectively. Results of the meta-analysis showed that the global prevalence of T allele and TT genotype were 24.0 % (95 % CI 21.7-26.5) and 7.7 % (95 % CI 6.5-8.9) respectively. In sub-group meta-analysis, the lowest frequency of T allele was found in Africans (10.3 %; 95 % CI 3.8-16.8), and highest in Europeans (34.1 %; 95 % CI 31.9-36.3). The frequency of T allele in the North India is 11 %. The results of the meta-analysis showed that the frequency of the T allele and the TT genotype of C677T is highest in the Caucasian population.

Genetic variation in the coagulation factor V gene and risk of femoral head osteonecrosis

Osteonecrosis of the femoral head (ONFH) is characterized by the death of the cellular portion of the femoral head due a reduction or disruption in the blood supply. Certain studies have implicated coagulation disorders, including thrombophilia and hypofibrinolysis, in the pathogenesis of ONFH. The factor V (F5) Leiden mutation has been suggested to be a genetic risk factor for venous thromboembolism and osteonecrosis in Caucasian individuals, however, this association remains controversial in other populations. The present study aimed to identify polymorphisms of the F5 gene and performed a case‑control study in a Korean population. The F5 gene was sequenced in 24 unrelated Korean individuals, and 16 polymorphisms were detected. A total of six polymorphisms were genotyped in 423 patients with ONFH and 348 control individuals. Analysis of the association between genotyped single nucleotide polymorphisms and haplotypes and with ONFH was performed. Comparison of the ONFH samples and the control individuals using logistic regression models revealed no statistically significant difference in the frequencies of the F5 polymorphisms and haplotypes. These findings suggested that F5 polymorphisms were not significant in the susceptibility to ONFH in the Korean population.

Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism: epidemiology, metabolism and the associated diseases

The Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism is associated with various diseases (vascular, cancers, neurology, diabetes, psoriasis, etc) with the epidemiology of the polymorphism of the C677T that varies dependent on the geography and ethnicity. The 5,10-Methylenetetrahydrofolate reductase (MTHFR) locus is mapped on chromosome 1 at the end of the short arm (1p36.6). This enzyme is important for the folate metabolism which is an integral process for cell metabolism in the DNA, RNA and protein methylation. The mutation of the MTHFR gene which causes the C677T polymorphism is located at exon 4 which results in the conversion of valine to alanine at codon 222, a common polymorphism that reduces the activity of this enzyme. The homozygous mutated subjects have higher homocysteine levels while the heterozygous mutated subjects have mildly raised homocysteine levels compared with the normal, non-mutated controls. Hyperhomocysteinemia is an emerging risk factor for various cardiovascular diseases and with the increasing significance of this polymorphism in view of the morbidity and mortality impact on the patients, further prevention strategies and nutritional recommendations with the supplementation of vitamin B12 and folic acid which reduces plasma homocysteine level would be necessary as part of future health education. This literature review therefore focuses on the recent evidence-based reports on the associations of the MTHFR C677T polymorphism and the various diseases globally.

Correlation of methylenetetrahydrofolate reductase polymorphisms with homocysteine metabolism in healthy Lebanese adults

Hyperhomocysteinemia is associated with several vascular and teratogenic conditions. Determinants of total homocysteine concentrations include genetic and nutritional factors. This study assesses the relation between homocysteine concentrations and MTHFR gene polymorphisms at two common alleles (C677T (rs1801133) and A1298C (rs1801131)) as well as other predictors of homocysteine (folate, vitamin B(12), body mass index (BMI), age, and gender) in a group of healthy Lebanese: 109 males and 124 females aged 17-55years. We used serum for the determination of homocysteine, folate and vitamin B(12) levels and blood drawn in EDTA tubes for molecular analysis of MTHFR polymorphisms. Hyperhomocysteinemia was present in 59/233 (25.3%) of the subjects, with male/female ratio of 1.95. Multivariable regression analysis showed that homocysteine levels were negatively related to folate and vitamin B(12) and positively related to male gender and C677T homozygosity; but not A1298C polymorphism, BMI or age. The prevalence of wild, heterozygous, and homozygous C677T genotypes was 45.0%, 43.3% and 11.6%, respectively; with a carrier frequency of 54.9% and allelic frequency of 33.3%. The A1298C genotypic prevalence was 39.5%, 30.9%, and 29.6% respectively; with a carrier frequency of 60.5% and allelic frequency of 45.1%. C677T/A1289C compound heterozygosity was present in 47/233 (20.2%) of volunteers. In this first pilot study, gender, folate, vitamin B(12) and C677T mutational status could explain around 32% of homocysteine variations. Future larger studies are recommended to investigate other predictors of homocysteine variation and combine them with markers explored in this and other studies, in order to evaluate their impact on vascular and/or congenital diseases.

Thrombus obstructing the right ventricle outflow tract in a neonate with methylenetetrahydrofolate reductase 677TT genotype

At her first day of life, a neonate presented with severe cyanosis and a mass obstructing the right ventricle outflow tract. Prostagladin E1 was necessary to provide pulmonary blood flow. The mass was removed using extracorporeal bypass surgery; the right ventricle was dilated, and the pulmonary valve leaflets were damaged. Sternal closure was delayed because of bleeding and poor cardiac performance. Histology demonstrated that the mass was a mixed thrombus. Investigation revealed homozygous 677TT genotype of the methylenetetrahydrofolate reductase. In conclusion, a life-threatening thrombotic event such as an intracardiac thrombus obstructing the right ventricle outflow tract can occur in a neonatal age. Since the event can be a result of a combination of acquired and congenital thrombogenic risk factors, an extensive screening including DNA-based mutation analysis should be performed.

Humans, mice, and mechanisms of intestinal atresias: a window into understanding early intestinal development

INTRODUCTION

Intestinal atresias have long been hypothesized to result from either failure of recanalization of the intestinal lumen or in utero vascular accidents. Recent work in animal models is now calling for a reassessment of these widely held paradigms.

PURPOSE

In this review, we will examine the data that led to the original hypotheses and then evaluate more recent work challenging these hypotheses. Furthermore, we will discuss how defining the mechanism of atresia formation in animal models may provide insight into early intestinal development and the mechanism of lengthwise intestinal growth.

CONCLUSION

Such insight will be critical in developing regenerative therapies for patients with intestinal failure.

Polymorphisms in theMTHFRgene and their possible association with susceptibility to childhood acute lymphocytic leukemia in an Indian population

Acute lymphocytic leukemia (ALL) is the most common pediatric cancer worldwide, and is particularly more common in the Indian population. Hence, research is increasingly examining the factors involved in disease development. In the present study, we examined the effect of MTHFR (5,10-methylenetetrahydrofolate reductase) C677T and A1298C polymorphisms in ALL. Blood samples of 135 children with ALL and 142 matched controls were analysed. The presence of MTHFR C677T and A1298C polymorphisms were screened using polymerase chain reaction-restriction fragment length polymorphism based approaches. The frequency of MTHFR 677CC, 677CT and 677TT genotypes were 37.77%, 57.03% and 5.18% in cases and 55.63%, 40.84% and 3.52% in controls, respectively. Frequencies of MTHFR 1298AA, 1298AC and 1298CC genotypes were 30.37%, 61.48% and 8.14% in cases and 45.77%, 47.88% and 6.33% in controls, respectively. The present study inidcates that there is an association between MTHFR gene polymorphisms and ALL. MTHFR variants also showed a gender bias. The frequencies of MTHFR 677CC and 677CT genotypes were 33.33% and 65.51% in males and 45.83% and 41.66% in females. Frequencies of MTHFR 1298AA, 1298AC and 1298CC genotypes were 26.43%, 67.81% and 5.74% in males and 37.5%, 50.0% and 12.5% in females, respectively. It is evident that the male children were more susceptible to ALL compared to female children. Associations found in these studies were significant with respect to gender bias; hence, it is possible that MTHFR C677T and A1298C can be good markers for ALL. Moreover, the possibility also exists that these variants may be influenced by the folate uptake of mothers during pregnancy, thereby influencing the enzyme activity and the ethnicity of the cases examined to date. The gender bias of MTHFR polymorphism in ALL is reported for the first time.

No Association of Factor V Leiden, Prothrombin G20210A, and MTHFR C677T Gene Polymorphisms With Kidney Allograft Survival: A Multicenter Study

BACKGROUND

It has been proposed that inherited risk factors of venous thromboembolism, such as factor V G1691A (FV-Leiden), prothrombin G20210A, and methylenetetrahydrofolate reductase (MTHFR) C677T, might be associated with poorer survival rates of transplanted kidneys. On the basis of this hypothesis, we performed a multicenter study, involving recipients of primary and repeat kidney transplants, to investigate the potential effect of these three single nucleotide polymorphisms (SNP) on graft survival.

METHODS

The study consisted of 676 first and 651 retransplant patients. Using the polymerase chain reaction-sequence specific primers method, we typed all patients for the three SNP and analyzed graft survival.

RESULTS

We could not find a statistically significant association between graft survival and factor V Leiden or MTHFR C677T genotypes. A better 3-yr graft survival was found for first transplant recipients with the genotype prothrombin 20210 G/G as compared to those with the G/A genotype (P=0.031). However, Bonferroni correction for the three SNPs investigated in this series rendered the P value insignificant (P(corrected)=0.093).

CONCLUSION

We did not find a statistically significant association of SNP factor V Leiden G1691A and MTHFR C677T with renal graft survival. Prothrombin G20210A resulted in a significant association that was not sustained after Bonferroni correction. This SNP might be an interesting candidate for future studies.

Primer-engineered multiplex PCR-RFLP for detection of MTHFR C677T, prothrombin G20210A and factor V Leiden mutations

Single-nucleotide polymorphisms in the genes that code for coagulation factors V (factor V Leiden) and II (prothrombin, G20210A), as well as the methylenetetrahydrofolate reductase (MTHFR, C677T) gene, have been implicated in the majority of cases of hereditary thrombophilia. We have developed a multiplex PCR-RFLP assay based on MnlI endonuclease digestion for the simultaneous detection of mutations in the FV, FII, and MTHFR genes. Digested amplification products were analyzed by gel electrophoresis in a single gel lane and visualized by ethidium bromide. This approach is a rapid and convenient method, hence economic, that alternate to others described for the detection of FVL, G20210A and C677T mutations.

A new PCR-SSP typing method for six single-nucleotide polymorphisms impairing the blood-clotting cascade as well as T-cell stimulation

Single-nucleotide polymorphisms (SNPs) within the genes of factor V (FV) (G1691A; exon 10), prothrombin (FII) (G20210A; 3'untranslated - region) and methylenetetrahydrofolate reductase (MTHFR) (C677T; exon 4) are associated with hypercoagulability, and systematic screening of individuals being at higher risk of thrombosis has been suggested. SNPs in the 2q33 region within the genes of CD28 (+17T/C; intron 3) and CTLA4 (-318C/T; promoter and +49A/G; exon 1) are likely to affect T-cell proliferation and antigen presentation signaling, which may lead to altered sensitivity of allograft or self-tissue recognition and affect the incidence of autoimmune diseases. We developed primers that allow specific amplification of these six SNPs at test conditions identical with those used for HLA typing with the CTS PCR-SSP reagents. One hundred ninety-six healthy German Caucasian individuals were tested for the six SNPs. The genotype frequencies for all SNPs were in Hardy-Weinberg equilibrium. There was no significant difference in the distribution of genotypes when compared to other published studies in which these SNPs were tested. The described PCR-SSP method can be used to screen large numbers of patients for these SNPs.

Evaluation of temperature gradient capillary electrophoresis for detection of the Factor V Leiden mutation: coincident identification of a novel polymorphism in Factor V

AIM

The Factor V Leiden mutation (G1691A) is a clinically important polymorphism that results in an increased risk of thrombosis. The goal of this study was to compare a temperature gradient capillary electrophoresis (TGCE) platform for the detection of Factor V gene mutations to a conventional restriction fragment length polymorphism (RFLP) assay.

METHODS

Three hundred and four samples were analyzed by both TGCE and a common clinical Mnl I/RFLP assay. Concordance of results between the two assays was observed for 302/304 (99.3%) of the samples.

RESULTS

All of the Leiden mutants (23/23, 100%) were identified by TGCE. Of the two discrepant results, one was caused by low peak heights in the TGCE output data and was easily rectified by the addition of a minimum peak height threshold. The second discrepancy resulted from the presence of a G-->A transition 95 bp downstream of the Leiden mutation site. This polymorphism represents a previously unreported alteration of the Factor V gene.

CONCLUSIONS

The TGCE assay is less labor-intensive and has a higher throughput capacity than the Mnl I/RFLP assay. TGCE is a less specific assay than the Mnl I/RFLP assay that allows for the detection of novel polymorphisms, but also creates the need for all positive TGCE results to be confirmed by an alternate method such as sequencing. Our results demonstrate that TGCE is a highly sensitive method for mutation detection and has utility for mutation discovery analysis.

RT-PCR permits simultaneous genotyping of thiopurine S-methyltransferase allelic variants by multiplex induced heteroduplex analysis

Thiopurine-based drugs are a widely prescribed group of medications. Their tolerance and effectiveness is dependent on an individual's ability to metabolize these compounds. An essential enzyme for the metabolism of these drugs is thiopurine S-methyltransferase (TPMT), whose activity is subject to genetic variation. Genotyping of the most frequent allelic variants in TPMT affords an extremely accurate prediction of the three clinical phenotypes: high, intermediate, and low enzyme activity. One constraint of most genotyping methods is the inability to demonstrate physical linkage between two sequence variants that occur in different exons, e.g., c.460G>A and c.719A>G, which give rise to TPMT*3, the most common defective allele in Caucasian populations. Using mRNA/cDNA as a template enables analysis of both sequence variants in a single assay. This approach could be applicable to other genes where allelic variation (in-cis and in-trans) is due to alterations in different exons. Induced heteroduplex generator analysis has previously been shown to discriminate in-cis and has also been suitable for multiplexing. In this method we have exploited both these features and for the first time have applied them to a RT-PCR analysis. The primary reagent developed allows unequivocal resolution of TPMT*3A and the alleles carrying the c.719A>G allelic variant, TPMT*3C, as well as the silent alteration c.474T>C. The TPMT*3B variant has not been observed. A secondary reagent, which can be multiplexed, identifies the TPMT*2 allele.

Large volume donor plasmapheresis in inherited thrombophilia implicated in arterial thrombosis

BACKGROUND

Life-threatening complications following apheresis are rare, and include venous thrombosis. Arterial thrombosis following apheresis has not been reported.

CASE REPORT

A 48 year old donor had cerebral infarction following large volume plasma donation. The outcome was fatal. He was found to be heterozygous for both methylene tetrahydrofolate reductase (MTHFR) 677C-T mutation and Prothrombin 20210G-A allele.

CONCLUSION

This case suggests that large volume plasma donation may trigger arterial thrombotic events in inherited thrombophilia. Therefore, the effects of plasmapheresis on coagulation system should be studied thoroughly.

Rapid automated simultaneous screening of (G1691A) Factor V, (G20210A) prothrombin, and (C677T) methylenetetrahydrofolate reductase variants by multiplex PCR using fluorescence scanning technology

The Factor V Leiden mutation (G1691A), and mutations in the prothrombin (G20210A) and 5,10-methylenetetrahydrofolate reductase (C677T) genes are common hereditary risk factors associated with venous thrombosis. The aim of this study was to develop an automated, PCR-based genotyping assay for rapid simultaneous screening of these three mutations. We adapted multiplex PCR, using primer modifications to introduce cleavage sites for restriction endonucleases into the fragments bearing each of the mutations. The three mutations were analyzed in a single tube by fluorescence scanning. An internal digestion control was introduced to prevent false-negative results due to incomplete digestion or a total lack of digestion. DNA fragment analysis was carried out using an automated capillary electrophoresis instrument (ABI310). This reliable, efficient, easy-to-use assay can be applied to specimens from large clinical trials and epidemiological surveys.

Mutations C677T and A1298C of the 5,10-methylenetetrahydrofolate reductase gene and fasting plasma homocysteine levels are not associated with the increased risk of venous thromboembolic disease

Mild hyperhomocysteinemia is associated with homozygosity for the thermolabile variant of 5,10-methylenetetrahydrofolate reductase (MTHFR) and could increase the risk of venous thromboembolic disease (VTD). Recently, the second A1298C mutation of the MTHFR gene was described. The present study aimed to analyze both mutations of the MTHFR gene and plasma homocysteine levels in subjects with VTD. The study groups comprised 146 patients with VTD and 100 healthy subjects. There were no statistical differences in carrier frequency and allelic frequency for both A1298C and C677T mutations, nor were there any differences encountered between subjects with VTD and controls in either plasma homocysteine levels or according to C677T or A1298C genotypes of MTHFR. In our VTD patients and controls, neither MTHFR 677CT/1298CC nor MTHFR 677TT/1298CC combined genotypes were observed; double heterozygotes (A1298C/C677T) were represented only in 11% of VTD patients, and in 15% of the controls. In conclusion, the polymorphisms C677T and A1298C of MTHFR and fasting plasma homocysteine levels do not seem to be significant risk factors for venous thromboembolic disease.

Factor V Leiden mutation screened by PCR and detected with lanthanide-labeled probes

The Factor V Leiden mutation is an important human polymorphism, responsible for increased risk of venous thrombosis in heterozygotes as well as homozygotes. Therefore, screening is a useful possibility, and many detection systems have been described for PCR products. We have developed a simplified and robust assay using oligonucleotide probes for normal and mutant sequences, labeled with europium and samarium, respectively, and measured by time-resolved fluorescence. Populations consisting of 233 Welsh and 148 Irish subjects were examined by both restriction fragment length polymorphism (RFLP) analysis and our assay. The allele frequency was 14/466 in the Welsh and 5/296 in the Irish population, in line with other surveys of European populations. Results were not obtained in 2/381 samples by RFLP, compared with 1/381 with our method. We conclude that our method represents an improved system capable of considerable throughput at reasonable cost.

Neonatal sinovenous thrombosis associated with homozygous thermolabile methylenetetrahydrofolate reductase in both mother and infant

The C677T mutation in 5,10-methylenetetrahydrofolate reductase (MTHFR) predicts substitution of valine for alanine at residue 223 (A223V). This thermolabile form of MTHFR has 50% reduced activity, has been associated with hyperhomocystinemia, and is a described risk factor for thrombosis in adults.(1-3) In addition, it has been associated with birth defects in the infants of affected mothers and with recurrent fetal losses.(4-6) We report the occurrence of sinovenous thrombosis in a newborn infant who presented with seizures. Both infant and mother were subsequently identified as having homozygous C677T alleles for MTHFR.

Thermolabile methylenetetrahydrofolate reductase (C677T): frequency in the Irish population

BACKGROUND

The genetic variation which underlies the thermolability and low enzyme activity of 5,10-methylenetetrahydrofolate reductase (MTHFR; C677T) has been extensively studied in many populations, including the Irish population.

AIM

To describe the examination of the C677T substitution in two new control samples drawn from the Irish population.

METHODS

A collection of 487 serum samples was obtained through the blood transfusion services of both the Republic of Ireland and Northern Ireland and a further 115 samples from volunteers.

RESULTS

In both samples, the frequency of the thermolabile/low enzyme activity allele (T) was higher than that previously reported for the Irish population.

CONCLUSION

This finding thus supports the need for a greater use of internal control/family-based association studies, as opposed to the classic case control study design, when assessing the contribution of the MTHFR T allele to disease processes.

An investigation of the association of the prothrombin G20210A gene mutation and inflammatory bowel disease: Factor II and IBD

BACKGROUND

A thrombotic etiology for inflammatory bowel disease (IBD) has been proposed as a result of its association with thromboembolic complications, smoking, the oral contraceptive pill, and the response of ulcerative colitis (UC) patients to heparin. We have previously demonstrated an increased prevalence of the Factor V Leiden mutation in UC and wished to investigate the frequency of the recently discovered prothrombin G20210A gene mutation in IBD. The aim of the study was to investigate the hypothesis that the prothrombic state associated with the prothrombin G20210A gene mutation is involved in the etiology of IBD.

PATIENTS AND METHODS

A prospective cohort study of patients attending the Bristol Royal Infirmary and Gloucestershire Royal Hospital's IBD clinics was performed. Thirty-nine patients with IBD (24 with Crohn's disease and 15 with UC) and 100 historical controls were screened for the presence of the prothrombin gene mutation using a heteroduplex-based polymerase chain reaction technique. None of the patients with IBD had a personal history of thromboembolism, while three of them had a family history.

RESULTS

No IBD patients had the prothrombin gene mutation compared with four (4%) controls (allelic frequency 2%).

CONCLUSION

There does not appear to be an association of the prothrombin gene mutation with IBD and therefore it is unlikely to be involved in the etiology of IBD.

Primary thrombophilia in Mexico. II. Factor V G1691A (Leiden), prothrombin G20210A, and methylenetetrahydrofolate reductase C677T polymorphism in thrombophilic Mexican mestizos

We have shown that in Mexican mestizo patients with clinical features of primary thrombophilia, 39% have activated protein C resistance phenotype, 5% protein C deficiency, and 2% protein S deficiency. In the present study, in a group of 37 thrombophilic Mexicans and 50 normal controls, we assessed the factor V G1691A (Leiden), the prothrombin G20210A, and the methylenetetrahydrofolate reductase (MTHFR) C677T gene polymorphisms. Four patients were found to be heterozygous for factor V Leiden, 5 heterozygous for the prothrombin 20210, 16 heterozygous, and 6 homozygous for the MTHFR 677. There were four individuals with co-segregation of alleles: two heterozygotes for the factor V Leiden/prothrombin 20210, one heterozygote for prothrombin 20210/MTHFR 677, and one heterozygote for prothrombin 20210/homozygote for MTHFR 677. For factor V Leiden, prothrombin 20210, and MTHFR 677 mutations, the allele frequencies were respectively 1% (+/-0.2%, alpha = 0.05), <1% and 51% (+/-5%, alpha = 0.05), with calculated relative risks for thrombosis of 5.94 (P = 0.08), >7.66 (P < 0.05), and 0.44 (P NS), respectively. In Mexican mestizo thrombophilic patients, the low prevalence of the factor V Leiden mutation (10.8%) and the high prevalence of the prothrombin 20210 mutation (13.5%) contrast with those identified in Caucasian thrombophilic patients (21% and 6%, respectively; P < 0.01). On the other hand, the high prevalence of the MTHFR 677 mutation gene both in normal controls (78%) and thrombophilic patients (61%) does not support a role of this mutation in the thrombogenesis of Mexican mestizo patients.

DNA technology for the detection of common genetic variants that predispose to thrombophilia

With the identification of common single locus point mutations as risk factors for thrombophilia, many DNA testing methodologies have been described for detecting these variations. Traditionally, functional or immunological testing methods have been used to investigate quantitative anticoagulant deficiencies. However, with the emergence of the genetic variations, factor V Leiden, prothrombin 20210 and, to a lesser extent, the methylene tetrahydrofolate reductase (MTHFR677) and factor V HR2 haplotype, traditional testing methodologies have proved to be less useful and instead DNA technology is more commonly employed in diagnostics. This review considers many of the DNA techniques that have proved to be useful in the detection of common genetic variants that predispose to thrombophilia. Techniques involving gel analysis are used to detect the presence or absence of restriction sites, electrophoretic mobility shifts, as in single strand conformation polymorphism or denaturing gradient gel electrophoresis, and product formation in allele-specific amplification. Such techniques may be sensitive, but are unwielding and often need to be validated objectively. In order to overcome some of the limitations of gel analysis, especially when dealing with larger sample numbers, many alternative detection formats, such as closed tube systems, microplates and microarrays (minisequencing, real-time polymerase chain reaction, and oligonucleotide ligation assays) have been developed. In addition, many of the emerging technologies take advantage of colourimetric or fluorescence detection (including energy transfer) that allows qualitative and quantitative interpretation of results. With the large variety of DNA technologies available, the choice of methodology will depend on several factors including cost and the need for speed, simplicity and robustness.

Severe digital necrosis in an elderly patient with heterozygous factor V Leiden mutation

We report an 81-year-old female with a heterozygous factor V Leiden mutation who developed purpura fulminans. Digital necrosis, a characteristic clinical feature of purpura fulminans was prominent. Purpura fulminans is more common in children and adult cases are rare. Of eight reported cases of purpura fulminans resulting from a heterozygous factor V Leiden mutation recorded in the literature, only two were in adults: 40 and 42 years of age, respectively. This is the first report of this condition arising in a patient in her eighties.

A new polymorphism in the human factor VIII gene: implications for linkage analysis in haemophilia A and for the evolution of int22h sequences

A new polymorphism in the human factor VIII gene has been localized and characterized. It is a biallelic, single nucleotide polymorphism located in intron 22 of the gene, within the 9.5 kb int22h-1 segment. The allelic forms are G (frequency 0.65) and A (frequency 0.35), giving a predicted rate of heterozygosity of 0.46. The polymorphism occurs within a CG dinucleotide and affects an MspI site (CCGG). Int22h-1 is duplicated twice extragenically at Xq28; both extragenic copies (int22h-2 and -3) are also polymorphic with respect to MspI. Investigation of 156 MspI [-] alleles, comprising 30 intragenic and 126 extragenic sites, indicated that all were due to A alleles and none had arisen by C to T transition within the CG dinucleotide. The intragenic MspI site (designated MspI A) is located 737 bases downstream of a previously described XbaI restriction fragment length polymorphism. Despite their close proximity, the polymorphisms are not in complete linkage disequilibrium; haplotype analysis in 85 factor VIII genes from a Caucasian population predicts an informativity of approximately 60% in linkage studies using both, compared with an informativity of approximately 47% in studies using either on its own.

The allele frequency of mutations in four genes that confer enhanced susceptibility to venous thromboembolism in an unselected group of New York State newborns

The frequencies of Factor V G1691A (FVL), prothrombin (PT) G20210A, 5'10'methylenetetrahydrofolate reductase (MTHFR) C677T, and methionine synthase (MS) A2756G (four mutations associated with an increased risk of venous thromboembolism [VTE]) were determined in a sample of approximately 1500 New York State residents. Dried blood spots from approximately equal numbers of Caucasians, African-Americans and Hispanics were anonymously obtained from the New York State Department of Health Newborn Screening Program. Following PCR amplification of dried blood spot DNA, allele-specific oligonucleotide hybridization was used to detect mutant alleles. The total number of individuals at increased genetic risk for VTE was 271 (17.5%) of the 1553 persons tested. Increased genetic risk was defined as the heterozygous state for FVL or PT and the homozygous state for the MTHFR or MS polymorphisms. Sixteen individuals had more than one genetic risk factor. The MS gene variant allele frequencies for African-Americans and Hispanics are the first to be reported. This report also provides an estimate of the variant PT allele in the largest group of Hispanics studied to date.

Familial thrombophilia and retinal vein occlusion

PURPOSE

To perform a pilot study on the prevalence of familial thrombophilia in all cases of retinal vein occlusion with no known risk factors.

METHODS

Over the 1 year study period 71 patients presented with a new diagnosis of retinal vein occlusion (age 28-90 years). Fifty-five (77%) were excluded because of local predisposing factors. The remaining 16 (23%) had a full risk factor history taken and blood investigations of rheological factors and thrombophilia including tests for the factor V Leiden mutation, prothrombin G20210A allele and hyper-homocystinemia.

RESULTS

Of those with no local predisposing factors, 3 patients had antiphospholipid antibodies, 3 had raised fibrinogen levels, 4 had hyper-homocystinemia and 1 was heterozygous for the Leiden mutation. Other lifestyle risk factors such as obesity, smoking and a positive family history of venous thrombosis were not uncommon. No patient had the prothrombin G20210A variant.

CONCLUSIONS

It seems likely that several risk factors, both genetic and acquired, need to be present for thrombosis to occur. In investigating a new patient with a retinal vein occlusion one should test for hypertension, glaucoma and diabetes mellitus. Estimation of plasma viscosity and a full blood count are cheap investigations which may reveal neoplasia or vasculitis, and lipid levels should be estimated. In a young patient or one with an unexpected vein occlusion and a personal or family history of thrombosis, a hypercoagulable state may rarely be identified. This additional testing should include testing for antiphospholipid antibodies and a full thrombophilia screen including the factor V Leiden mutation, homocysteine and the prothrombin variant as part of a clinical trial. Until the role of these markers in thrombosis is better defined in relation to causation of retinal vein occlusion and treatment has been shown to improve outcome, we can not recommend them for routine testing. If a hereditary defect is found, referral should be made to a hematologist and consideration given to anticoagulation and screening of family members to prevent further thrombotic episodes. Retinal vein occlusions are multifactorial in origin except in rare cases.

Polymorphisms in the methylenetetrahydrofolate reductase gene are associated with susceptibility to acute leukemia in adults

Reduction of 5,10-methylenetetrahydrofolate (methyleneTHF), a donor for methylating dUMP to dTMP in DNA synthesis, to 5-methyltetrahydrofolate (methylTHF), the primary methyl donor for methionine synthesis, is catalyzed by 5,10-methylenetetrahydrofolate reductase (MTHFR). A common 677 C --> T polymorphism in the MTHFR gene results in thermolability and reduced MTHFR activity that decreases the pool of methylTHF and increases the pool of methyleneTHF. Recently, another polymorphism in MTHFR (1298 A --> C) has been identified that also results in diminished enzyme activity. We tested whether carriers of these variant alleles are protected from adult acute leukemia. We analyzed DNA from a case-control study in the United Kingdom of 308 adult acute leukemia patients and 491 age- and sex-matched controls. MTHFR variant alleles were determined by a PCR-restriction fragment length polymorphism assay. The MTHFR 677TT genotype was lower among 71 acute lymphocytic leukemia (ALL) cases compared with 114 controls, conferring a 4.3-fold decrease in risk of ALL [odds ratio (OR = 0.23; 95% CI = 0.06-0.81]. We observed a 3-fold reduction in risk of ALL in individuals with the MTHFR 1298AC polymorphism (OR = 0.33; 95% CI = 0.15-0.73) and a 14-fold decreased risk of ALL in those with the MTHFR 1298CC variant allele (OR = 0.07; 95% CI = 0.00-1.77). In acute myeloid leukemia, no significant difference in MTHFR 677 and 1298 genotype frequencies was observed between 237 cases and 377 controls. Individuals with the MTHFR 677TT, 1298AC, and 1298CC genotypes have a decreased risk of adult ALL, but not acute myeloid leukemia, which suggests that folate inadequacy may play a key role in the development of ALL.

Multiplex analysis of mutations in four genes using fluorescence scanning technology

Multiplex analysis of genetic mutations using fluorescence scanning methodology is an accurate, efficient, and cost-effective approach to genotypic characterization. Fluorescence labeling during the synthesis of polymerase chain reaction primers allows the application of this technology to well-established protocols. We have simultaneously analyzed the four polymorphisms of factor V Leiden (G1691A), prothrombin G20210A, 5,10-methylenetetrahydrofolate reductase C677T, and cystathionine beta-synthase 844ins68. Three of these mutations have been associated with an increased risk of thrombosis. Following polymerase chain reaction with fluorescence-labeled primers, the polymerase chain reaction products were digested with an appropriate restriction enzyme (if necessary for detection of the mutation), diluted into one tube per sample for co-loading (multiplex loading), and analyzed with GeneScan software for fragment analysis following capillary electrophoresis on an ABI PRISM 310 Genetic Analyzer (Foster City, CA, USA). Multiplex loading increased throughput without compromising precision.

Factor V Leiden and the common haemochromatosis mutation HFE C282Y: is there an association in familial venous thromboembolic disease?

The involvement in venous thrombosis of the two most common mutations of the hereditary haemochromatosis gene (HFE C282Y and HFE H63D) was investigated in 239 patients with objectively proven venous thrombosis. Neither mutation showed an increased prevalence in the cohort (HFE C282Y: 13.0% (95% CI 9.3-17.8) patients, 16.2% (95% CI 14.3-18.2) controls; HFE H63D: 28.3% (95% CI 22.9-34.3) patients, 28.1% (95% CI 25.8-30.6) controls. Neither mutation was increased in patients with factor V Leiden (FVL) compared to those without. However, HFE C282Y was increased among patients who had both FVL and a family history of thrombosis (7/20), compared with those with FVL and no family history (1/22) (relative risk 7.97, 95% CI 1.5-43.1, P = 0.016).

A novel ELISA-based primer extension assay for the detection of the factor V Leiden mutation

We describe an enzyme-linked immunosorbent assay (ELISA) based primer extension method for the detection of the factor V Leiden (FVL) mutation. The wild-type nucleotide at position 1691 or the mutant nucleotide at the complementary position on the antisense strand were detected by the incorporation of biotinylated complementary bases onto fluorescein isothiocyanate (FITC) labelled mini-sequence primers with specificity for the sense and antisense gene segments downstream from the bases adjacent to position 1691. The reactions took place in pairs of tubes containing the complementary bases to either the wild-type or mutant nucleotide respectively. Primer extension products from each reaction tube pair which have incorporated biotinylated bases were then captured in streptavidin-coated microtitre plate wells and detected colourimetrically using an ELISA procedure. 200 patient samples were tested to validate the assay and there was complete genotypic agreement between the ELISA method and restriction site analysis using Mnl I (137 wild type, 55 FVL heterozygotes and eight homozygotes). The method utilizes non-radioactive reagents and does not require electrophoretic techniques. It is therefore a safe, simple and rapid assay which lends itself to automation.

Development of an internal restriction control in the PCR detection of the prothrombin 20210A mutation

Detection of the presence of the 20210A/G allele in the human prothrombin gene is easily achieved by amplification using primers designed to span this region. The downstream primer creates a HindIII restriction site if the 20210A variant is present. A new forward upstream primer was designed to incorporate a naturally occurring HindIII site that, as it is present in both alleles, serves as an internal restriction control. Using this technique, the DNA of 292 unselected patients with venous thromboembolic disease was analysed. Of the 149 white patients, 4.7% were heterozygous for this mutation but none of the African Black patients were positive.